cpufreq: Extend ondemand powersave_bias for negative range

Original ondemand powersave_bias parameter allows value
range from 0 (no powersave) to 1000 (100% reduction in
calculated CPU frequency).  This change extends powersave_bias
into the negative range (-1 to -1000) to allow a corresponding
boost to CPU frequency.  When set at either limit (-1000 or
1000), ondemand timer is cancelled as periodic load
sampling at sampling_rate is not necessary.

Change-Id: I2ee05729ceec20c2e2a4c6d9ca05cecd16ab161a
Signed-off-by: David Ng <dave@codeaurora.org>